swift234

When applying an operator found in a protocol, compute the effetive
base type (e.g., the archetype type, when we're in a generic function)
used to refer to that operator as a member, e.g., given

  func min<T : Ord>(x : T, y : T) {
    if y < x { return y } else { return x }
  }

'<' is found in the Ord protocol, and is referenced as

  archetype_member_ref_expr type='(lhs : T, rhs : T) -> Bool' decl=<
    (typeof_expr type='metatype<T>'))

using a new expression kind, TypeOfExpr, that simply produces a value
of metatype type for use as the base.

This solves half of the problem with operators in protocols; the other
half of the problem involves matching up operator requirements
appropriately when checking protocol conformance.


Swift SVN r2443